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Message: <blockquote data-quote="SG6" data-source="post: 1272906" data-attributes="member: 68155">I am a little wary of the term LD glass, simply because to design and build a doublet lens the 2 glass components have to have different refractive indexes. The lower refractive index glass also therefore has a lower dispersion then does the higher refractive index glass.The use of Crown and Flint glass to make a cheap doublet means that the Crown component is the "LD" component. But I would not count Crown glass as a real "LD" glass. Seems that ice would made a good LD component but has a habit of melting.<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />So any doublet lens at the front of a set of binoculars can to some extent claim to have an LD component.o<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite8" alt=":D" title="Big grin    :D" loading="lazy" data-shortname=":D" /> and I suspect that the marketing people have already latched on to this.What is not advertised is that a lower dispersion glass will need to have a more curved set of faces in order to attain the required focal length and this introduces more spherical abberations. You could get a nice colour balanced fuzzy image therefore.:-OChartwell's comment of weight of an apochromatic set of binoculars makes sense, the front objective will be a triplet built of 3 types of glass - more glass = more weight and the weight is at the front and has a greater effect when holding them. Each glass component is there to colour correct for a separate wavelength. Wonder which wavelengths the different manufacturers build their lenses for? That would be interesting and may explain why some people find one make better then another.As for Henry saying no binoculars have apochromatic lenses if the manufacturer has built, or uses, a triplet lens for colour correction at 3 different wavelengths then it is a apochromatic lens. It may be good or bad, may work with the remaining optics of the binocular or not, but it is a apochromatic lens.They are probably in binoculars as they have been around for years, I was building systems with them 25+ years back and aren't exactly expensive, but are a good marketing ploy, and some of them may work.:eek!::eek!::eek!:A well designed doublet with good components will probably give better results then a mediocre triplet, but the triplet ultimately has more protential.The other thing I see that never comes into the overall performance is mention of one optical component that we have little control over, is a necessary component and that basically is a simple single lens system that is supposed to handle all situations, near, far, bright, dark, all wavelengths and deteriorates with time. The human eye. The bin's I have do not quite handle my eyes so I need to use glasses with them and I have a small astigmatism correction which not even the most expensive binoculars can compensate for.</blockquote>

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